Paleoclimatic Significance of the Mineral Magnetic Record of the Chinese Loess and Paleosols

Quaternary Research - Tập 37 Số 2 - Trang 155-170 - 1992
Barbara A. Maher1, Roy Thompson2
1School of Environmental Sciences, University of East Anglia, Norwich, United Kingdom
2Department of Geology and Geophysics, University of Edinburgh, United Kingdom

Tóm tắt

AbstractThe origins of the magnetic susceptibility variations of the Chinese loess and paleosols are explored by scanning and transmission electron microscopy of magnetic extracts, and by magnetic modeling of magnetic hysteresis data, to provide quantified estimates of the major magnetic components. Microscopy identifies several distinct size and shape characteristics in the magnetic carriers. Lithogenic magnetites, intact and abraded, dominate the coarse-grained magnetic fraction. The smallest of the coarse grains is ∼ 2 μm. The remaining magnetic materal is ultrafine in size, with two types of magnetite particles present. Type A particles strongly resemble soil magnetites produced by inorganic precipitation. Type B particles, which occur rarely, are probably bacterial in origin. Quantitative modeling of these magnetic assemblages shows that over 90% of the susceptibility variations is accounted for by the superparamagnetic magnetite component. Compared to the loess units, the paleosols are richer in magnetite, particularly of superparamagnetic size, and have a threefold higher ratio of magnetite to hematite. We identify pedogenic formation of magnetite as the major contributor to the loess magnetic record. Matching this record against other paleoclimatic records, we find an extremely high correlation with the standard 18O record. The Chinese loess sequences record a very high resolution magnetic stratigraphy directly related to changing climate.

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Tài liệu tham khảo

10.1016/0277-3791(87)90004-7

10.1080/00018736300101263

10.1016/0012-821X(91)90168-H

10.1038/300431a0

10.1016/0012-821X(82)90141-8

10.1016/S0031-9201(86)80013-9

10.1130/0091-7613(1988)016<0811:PCICDB>2.3.CO;2

10.1038/346737a0

10.1130/0091-7613(1991)019<0003:MMROTC>2.3.CO;2

Thompson, 1986, Environmental Magnetism, 10.1007/978-94-011-8036-8

10.1111/j.1365-246X.1988.tb03429.x

Imbrie, 1984, The orbital theory of Pleistocene climate: Support from a revised chronology of the marine delta 18O record, 169

10.1130/0091-7613(1990)018<0040:PFOMSV>2.3.CO;2

10.1029/GL013i011p01169

10.1017/S0370164600032181

10.1007/BF00202045

10.1038/336368a0

10.1016/S0031-9201(86)80006-1

10.1038/343161a0

10.1038/330252a0

Radhakrishnamurty, 1974, Magnetic techniques for ascertaining the nature of iron oxide grains in basalts, Journal of Geophysics, 40, 453

10.1029/RG010i001p00213

10.1038/263490a0

10.1111/j.1365-246X.1984.tb01928.x

10.1029/PA005i002p00109

10.1038/256565a0

10.1111/j.1365-246X.1986.tb04522.x

10.1038/340296a0

10.1180/claymin.1987.022.4.05

10.1038/299538a0

Prell, 1991, One Million Year Record of Summer Monsoon Winds and Continental Aridity from the Owen Ridge (Site 722), Northwest Arabian Sea, 365

10.1146/annurev.mi.36.100182.001245

10.1038/342897a0

10.1038/320611a0

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Quaternary Research

Tập 37 Số 2

155-170

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